1. Technical Field of the Invention
This invention relates to digital power amplifiers and, more particularly, to a digital power amplifier suited for apparatus size reduction.
2. Description of the Related Art
In recent years, rapid progress has being made in digitalizing the amplifiers for power amplification. Particularly, real adoptions are conspicuous in the audio amplifiers. The appliances mounted with digital power amplifiers (so-called switching amplifiers) include DVD players, mini-compo stereo sets, television receivers, personal computers and so on. Furthermore, considerations are given also toward the adoption to the cellular phones under functional improvement.
This is to cope with the requirement of reducing the size or consumption power in the audio amplifiers having increased by the functional improvement in these appliances,
On the other hand, the digital power amplifier using the conventionalxc2x1power source avoids the increase in the charging voltage to the power-source capacitor by a regenerative current on a low-pass filter (LPF) coil. In order to secure a stable operation in a low range having increasing regenerative current, there is a need for a chemical capacitor to have a large capacitance.
The chemical capacitor has a capacitance value directly involved in the low-range reproduction capability, and has generally an increased volume. This has been a factor to inhibit against the size and cost reduction of the apparatus.
FIG. 4 is a block diagram showing a configuration of a 1-bit digital power amplifier of a conventional scheme configuring output unit by a single power source. In this configuration, a signal processing circuit 101 compares an analog voice signal with a triangular wave inputted to an inverted input terminal (xe2x88x92). Namely, the analog voice signal is converted, with the triangle wave as a threshold, into a 1-bit digital signal. The converted digital signal is supplied to a driver of a switching section 105, to control the opening and closing of switches SW1, SW2, SW3 and SW4. The current, supplied from a power source (E) 109 of a power source section 107, flows in a direction passing the switch SW1, the load 111 and the switch SW3 or in a direction passing the switch SW4, the load 111 and the switch SW2. The load 111 is supplied with a digital alternating-current power, i.e. so-called a BTL connection. In this operation, concerning the affection of a regenerative current due to an LPF coil, because the charge to one capacitor and the discharge to a load are alternately done, capacitor voltage increase can be avoided. In this configuration, however, because load output is not grounded, there is a disadvantage that restricted are a plurality of connections with loads and appliances.
Meanwhile, the impossible output grounding is a serious defect of a DC output amplifier and power source.
However, high output, high efficiency and low power consumption are sought by the size-reduction and functional improvement in cellular phones, together with further size reduction toward digital audio amplifiers.
The present invention has been made in view of the foregoing problem. The problem lies in that the output can be grounded with a single power source, in order to provide a digital power amplifier making possible high output, high efficiency and low power consumption together with the size reduction in the digital audio amplifier.
Electrical isolation is provided between input and output sections by a photo-coupler on a transmission passage for turning into a digital signal. This enables a BTL output to be grounded.
In order to achieve the foregoing object, various exemplary embodiments according to the present invention provide: four switches SW1, SW2, SW3 and SW4 connected in an annular form; a load connecting section provided between a connection point of adjacent switches SW1 and SW2 and a connection point of adjacent switches SW3 and SW4 to connect a load; a power source connecting section provided between a connection point of adjacent switches SW1 and SW4 and the connection point of adjacent switches SW2 and SW3 to apply a voltage; a grounding section grounding the connection point of the adjacent switches SW3 and SW4; signal processing unit for converting an input signal into a 4-line digital signal; driving unit for controlling opening-and-closing drive of the switches SW1, SW2, SW3 and SW4 according to a digital signal supplied from the signal processing unit; isolating unit for electrically isolating between the signal processing unit and the driving unit; and feed-back unit for feeding back a signal at the connection point of the adjacent switches SW1 and SW2 to the signal processing unit.
In the invention, of the four switches annularly connected, a load connecting section is provided between the connection point of adjacent switches SW1 and SW2 and the connection point of adjacent switches SW3 and SW4, to provide here a load such as a speaker. Meanwhile, a voltage, e.g. E, is applied to a power source connecting section provided between the connection point of adjacent switches SW1 and SW4 and the connection point of adjacent switches SW2 and SW3. Also, electrical isolation is provided between the signal processing unit for converting an input analog signal and digital signal into a 4-line digital signal and the driving unit for controlling opening-and-closing drive of the switches SW1, SW2, SW3 and SW4 according to a digital signal supplied from the signal processing unit. On the other hand, the connection point of the adjacent switches SW3 and SW4 is grounded, a signal at the connection point of the electrically-isolated switches SW1 and SW2 to be fed back to the signal processing unit is enabled.
In various exemplary embodiments according to the invention, the isolating unit is a photo-coupler.
In this invention, the photo-coupler is used to once convert an electric signal into a light signal and furthermore into an electric signal, thereby completely electrically isolate between the signal processing unit and the driving unit.
In various exemplary embodiments according to the invention, the digital power amplifier is provided with a resistance having a value smaller than the load in series with the load connecting section, and changed to a constant-current-output digital power amplifier for feeding back a current flowing the load to an input side, a plurality of which are connected in parallel with one another.
In this invention, the digital power amplifiers in plurality are connected in parallel with one another thereby making them possible to supply a power having a magnitude multiple times in accordance with the number thereof.
In various exemplary embodiments according to the invention, the constant-current-output digital power amplifiers are connected at inputs and outputs into parallel connection, an input amplifier being provided in front of an input section of the parallel connection to feed back a voltage at an output section of the parallel connection to an entirety.